Measuring system



@attentati Nov. 19, 1946 UNTED STATES PATENT OFFICE MEASURING SYSTEM Sylvania Application March 23, 1944, Serial No. 5275786 (El. '7S-209) 1e claims. l

@ur'invention relates to measuring systems of tire type in which a magnetizable core structure is moved in response to changes in magnitude of a condition under measurement correspondingly to vary the relation to each other of the induct ances or coils in different branches of a balanceable electrical network; and more particularly relates to differences in characteristics of the coils 'for rendering the network for certain purposes adaptable for metering or indicating magnitudes of a condition, including rates of iiow ci iiuids, sucio. as fuels in general, including those utilizable iorproduotion of motive power for any purpose, and more especially for driving aircraft and other vehicles.

ln accordance with our invention, there is provided a balanceable electrical network in different arms or branches whereof are included inductlvely reactive coils so unlike as to differ from each other, especially in their structural characteristics, and so disposed relative to each other and a therewith coacting magnetic core structure, that the network partakes of certain useiul characteristics; and in other arms or branches of the network are disposed impedances, non-reactive or reactive, complemental to the impedances oi aforesaid arms, and the relation to each other of whose magnitudes is variable to effect balance ci tlie network; and, more particularly, with a graduated or calibrated scale of a meter, related to the network, there co-operates an index movable in unison with, or in dependence upon the movement of, a member actuated for balancine the network by varying the relations to each other or aforesaid magnitudes of said last-named reactive or non-reactive impedances; further in accordance with our invention a galvanometer which indicates balance of the network also indicates small informative imbalances thereof.

Further in accordance with our invention the markings or calibration divisions of aforesaid meter scale are spread or contracted in different portions or regions of the scale in dependence upon or as predetermined by the effect upon said network of aforesaid diierences in the characteristics of aforesaid coils and related core structure.

Our invention resides in measuring systems and apparatus of the character hereinafter described and claimed, and generally exemplified by the particular system hereinafter described.

For an understanding of our invention, reference is to be had to the accompanying drawings, in which:

Fig. i is a diagram oi a network;

Figs. 2-6 inclusive illustrate various meter :bnl scale-s diering with respect to the spacing of their calibration markings;

Figs. 'l and are schematic representations o3 coil-core assemblies, differing from the coll-core assembly ol Figs. l and 9;

Fig. 9 is a vertical sectional view of a unit coinprlsing flow-meter structure associated with a coilcore unit;

Fig. l0 is an elevational view ci a meter unit;

Fig. li is a vertical sectional view, on larger scale, oi a portion ot the meter unit shown in Fie. l0; and

Fig. l2 is a fragmentary elevational view oi parts shown in Fig. il.

Referring to Fig. l, the balanceable network N comprises, in diierent arms thereof, Iwithin the portion which is designated 'lransmitter, tire coils', reactive impedances, L and Lig, (whose noninductive resistances are Rt' and Re, respectively) and the co-operatinemagnetie core structure C; tbe core structure C (of iron, nickel or other suitable magnetic :metal or alloy) usually is the movable member, actuated or moved with respect to the coils in accord wltl'i'variations of the magnitudes of a condition to be measured to affect the inductances of the coils; for example, as shown in Fig. 9, core structure C is moved vertically with respect to the aligned coils Li and L by means constituting the responsive element or system oi a flow-meter, whereby in response to increases and decreases in the rate of :dow of a fluid, the core structure C rises or falls, thereby changing its positional and electromagnetic relation to tlie coils Li L.

in other arms of the network are included different portions, as determined by adjustment oi contact K, of an impedance R2, which may be reactive but which, by preference, is a non-in= ductive resistance for rendering the portion of tire network marked Receiven the meter unit, more compact, a matter of advantage when the system is utilized upon or in the cockpit oi an aeroplane, or in analogous situations where utmost compact-1 ness is desired.

The impedances Rl, R3 and Re may be nonreactive resistances, provided principally for calibrating the arms of the netwerk in which. they are connected.

One of the conjugate conductors extends from E, the common terminal of neighboring arms (of the network) in which coils L and Li respec-= tively are connected, to and terminates in afore`= said contact E adjustable along the-impedance R2 to effect balance or imbalance of the network by including ln different branches thereof dit ferent amounts of that impedance. The contact K may serve also as a pointer movable along a scale SI calibrated in units of rate of flow or in terms of the varying magnitudes of any other condition to 'be measured. Or, and preferably, with the contact K is associated and movable in unison therewith a pointe;` or index Kl movable with respect to a stationary scale S in the meter unit, Figs. 10 and 11. A source of alternating current A is connected in series in aforesaid conjugate conductor, preferably in the portion thereof in the Transmitter; in the same conductor may be included a generally small resistance R'l, to hold at suitably low magnitude the strength of current through the field windings 15 F, F of the galvanometer if that instrument should be of too high sensitivity. In the other conjugate conductor, extending from 2 to 3, is connected the coil G, of aforesaid galvanometer, mounted for rotation upon and about the axis of pivots P, p, With provision of a spring or equivalent, not shown, which biases the coil G toward and to its position corresponding with and representative of zero current therethrough, indicative of balance of the network or bridgeN. The

field coils F, F of the galvanometer are con-` nected in series with each other in circuit with source A; and in series with the field coils is connected a condenser M of capacity to bring into phase with each other the current through the galvanometer eldcoils F, F and the current through deflecting coil G.

Attached to and deflected by galvanometer coil G is an indicating member P, such as a pointer, which coacts with a mark i; the network is in .balance when the end (Pl, Fig. 11) of pointer P is in radial alignment with the mark i; for at least small unbalances of /the network, PI lwill lie on one side or the other of mark z', so indicating unbalances informative regarding certain conditions; for example, as indicated in Figs. 1 and 10, whether the amount of gasoline-air mixture delivered to a motor-is either rich or lean. Beyond such generally informative indications, the galvanometer deflections are not themselves measures of the magnitudes of the condition to be measured; those magnitudes are measured or predetermined by the positions of l contact K along impedance R2.

The current source A may, especially on aircraft, be one utilized also for other purposes including, for example, supply of current for radio apparatus.

The frequency of the alternating current supplied by source A for the 'general purposes of our invention is not of importance. On aircraft the frequency of that current may be for example 400 cycles per second, as may be required or desirable for any apparatus other than that of the present invention, such as aforesaid radio apparatus.

As shown in Figs. 1 and 9, the neighboring ends of coils L and Ll are close to each other. However as indicated in Figs. 7 and 8 these coils may be substantially spaced from each other, axially. Their windings may be of any suitable conductor, of number of turns and distribution thereof longitudinally of each coil to effect suitable or desired inductance thereof; the` number of turns of the coil Ll per unit of length thereof-may be uniform, or, preferably, greatest at or adjacent, or increasing in approaching, its end which is nearest the associated coil L.

In Fig. 7 the magnetic core structure Cl may be unitary or, as in Fig. 8, it may comprise two 'separate core elements or members C2 and C3 measurement.

In general the inductances of the coils L and Ll are or may be substantially equal'. When the frequency of the current supplied by source A (whose voltage, for example, may be 24 volts) is 400 cycles per second, an inductance of each of the coils L and Ll of the order of 0.1 henry is satisfactory, lbut may be of any other suitable magnitude; and the non-inductive resistances of those coils may be equal or substantially so, and of the order, for example, of about 85 to 90 ohms- R5 of coil LI-and, in the case of coil L, its noninductive resistance, R4, plus the resistance R6 (if needed for the purpose of rendering substantially equal the non-inductive resistances of the neighboring bridge arms) may be of about the same order, about 85 or 90 ohms. In the receiver the resistance RI may be of the order of about 50 or 55 ohms; R2 of the order of about 205 or 210 ohms; and R3 of the order of about 35 ohms.

In accord with this invention the coils L and Li, whether closely positioned as in Figs. 1 and 9 or spaced from each other as in Figs. 7 and 8, diier substantially from each other in length, as to an extent connoted by the fact their lengths mall, for example,` be about 4'1/2 inches and 21/2 inches, respectively. The length of the coacting core structure and its length of travel are related to the coils of different lengths and their relative positions; for example, the length of core C or CI, or the length from the top of core element C2 to the bottom of element C3, Fig. 8,

may be about 5 inches, and length of its travel the lower portion of the core structure is still preferably well within the 'lower coil Ll, as within a portion thereof having aforesaid greater or greatest number of turns per unit of length.

The core structure, unitary or composite, preferably is longer than the longer of the coils, whereby, as hereinafter noted, there always shall be some portion of the core structure, whatever its length of travel, simultaneously within both coils. And the length of the core structure and its length of travel are dependent upon or are determined by what shall be the total length of the scale (whether straight, as in Fig. l, or arcuate as in Figs. 3-6 inclusive and Fig. 10); or, conversely, the length of the core structure and its length of travel determine what shall be the total length of such scale, whether straight or arcuate.

Upon the lengths or relative lengths of the coils L and Ll, and upon the length and travel of their associated cor'e structure, and upon the reactances or relative reactances of the impedances of the adjacent bridge or network arms in which the inductances of coils L and Ll are respectively connected and effective, depends the openness of the scale, i. e., the magnitudes of the spacing, between the scale markings, per unit, or per equal number of units, of the magnitude of the condition to be measured; and the uniformity of the scale, in the sense of degree of equality of scale-mark spacings is dependent upon the same factors. Change in any of those fac tors, or change in the relation of any one or two with respectv to the others or other, will modify -the openness of the scale and/or the position between the ends of the scale' of the region of its greatest openness.

Fig. 2 illustrates a scale, of any arcuate length, for example about 270, which is practically uniform with respect to the scale divisions at both end regions as well as in the middle region. Such uniformity would obtain were the coils L and LI of equal lengths, accompanied by suitable length of the core structure cooperating therewith. In contrastA with the uniformity of the scale of Fig. 2, the scales of Figs. 3, 4 to 6 inclusive and l in accord with our invention for example about 1A; of its total length, in which there is preserved sucient uniformity, with, more importantly; increased openness or expansion affording high accuracy. ln briei, by our coils L and Ll of substantially different lengths and their related core structure and its length of travel, importantly greater precision is made possible in predetermining or measuring maghi tudes of a condition within at least any desired large portion of the entire range oi such magu nitudes.

In' Fig. ld the regionoi expansion or accentuated lopenness or scale isthe mid portion or section thereof, the magnitudes within which are those of 'vital or greatest importance to a pilot or the operator; in the end sections of the scale, to either side of the mid-section there4 is less openness, in the sense the scale markings arel relatively more, but harmlessly, compressed.

In Fig. 3 the scale markings are close or relatively compressed at the low magnitude or left end, and their spacings progressively increase to the right end where the scale is most expanded.

Fig. e represents a situation the reverse of Fig.

3, in the sense the scale is of greatest expansion at the low magnitude or lower left, and become progressively more compressed to the other or high reading end of the scale.

Fig. 5 represents a scale in which the midregion or section is compressed, while in both end sections the scale markings are/widely spaced from each other.

Fig.v 6 illustrates a type of scale procurable by coil spacing and core structures illustrated in `Figs. '7 or 3; it corresponds in general character with come S ol Fig. l0.

Fig. 9 illustratesan example of application ci our invention as applied, for example, to measuring or predetermining rates of flow oi a liuuid; it comprises the lower metal housing unit of the dow meter unit E, having the conical kupwardly divergent passage H extending from approximately the region or point Sl to approxi-- mately the point or region l@ where it opens into and communicates with the space l l with which is connected the discharge pipe l2, which delivers the liquid to destination, as to an aeroplane pro= peiling means, such as an internal combustion motor, or for jet propulsion. Secured to the upper end of member 8 is the metal member I 3, in which is provided at least a large part of aforesaidcavity Il. Upon the member l3kis disposed a tubular housing member I4 which may be of metal and in any event of such metal or material and dimensions (especially thickness) as will prevent or minimize production therein of eddy currents due to the stray alternating magnetic fields produced by the coils. Member I4 is surmounted by the cap- !5 upon which engages a nut I6 threaded upon the upper end of the guide rod il on which is vertically movable the tubular magnetic core C movable axially of the solenoids or coils L and Li. To prevent A affecting the accuracy or sensitivity of the iiowmeter, or the like, core C is as light in weight as possible consistent with its effective coaction with the coils. The coils surround tubular nonconducting member Ma, which extends in and to the bottom of member i3. The fixed guide rod il continues down beyond member ld through the chamber H, and on whose lower end is threaded nut i8 which holds in place a sleeve i9 through which the guide rod il extends, and upon which are disposed radially extending varies t@ for centering sleeve it in chamber El, in the llower end of housing d. The mouth of chamber 2l is provided with pipe threads to receive the threaded end of a pipe which delivers the liquid in question into member il at rate determined by manually or automatically controlled throttle or the like in advance of the discharge into chamber 2i and/or subsequent to discharge from member i2. Resting upon the fixed sleeve member l@ is the hollow movable member 22, sometimes termed a top or sinken closed at its bottom, and sealed at its top by the member 23 having a downwardly and outwardly tapered circumference coming to a sharp circular edge at or near the level 9, the portion of smallest diameter of the divergent passage H. The core structure, such as C, or other core structure herein referred to, is attached to the member 23 through the medium of an open cage Ell, of non-magnetizab-le material or metal, loosely fitting or disposed about non-magnetizable guide rod ll.

The liquid flows upwardly through passage l-l, into space tl and thence through conduit l2. ln so doing the member 22 rises and cornes to a position, above its illustrated position, of equilibrium for each oi the rates of flow in the range for which the structure is designed and suited. For each of the positions of equilibrium of member 22, the core structure C takes a definite position with respect to coils Ll and L, throughout the range of movement oi member 22 whose uppermost limit is adjacent the level ld.

'With low metering means of the particular character described, the extents of vertical movement of member 22 and core C are a linear func- 'tion of, directly proportional to, the magnitudes oirate oi i'iow; our invention also comprehends, however, means responsive to changes in magnitude oi a condition which are not a linear function of the movements of the core structure. In either case each change in core position is accompanied by a change in the ratio to each other ci the incluctances of the coils.

ln consequence of the difference between the lengths of the coils L and Ll, notwithstanding their inductances may be equal, and the resisttances (including the resistances of the coils) of neighboring arms or' the network N are equal, the scales, Figs. 3-6 inclusive and Fig. l0, are, in contrast with the uniform scale of Fig. 2, non-uni- 7 y form and in a chosen section or sections expanded, as hereinbe'fore noted; so making it possible, particularly because of the diierence in the lengths of the coils L and Ll, whether abutting each other as in Figs. 1 and 9 or spaced from each other as in Figs. 7 and 8, to eiect maximum openness or expansion of the scale at any region or regions thereof necessary for higher` or vital accuracy in metering and for vital or high precision in reading of the scale, as may be appropriate or required ior different needs or circumstances dependent upon the nature and purposes o various measuring systems whatever the nature and characteristics of their means responsive to changes in magnitude of the condition to be measured.

In' aircraft operation, for example, the rate of consumption of fuel is of great importance and must be precisely set or predetermined, and-must be precisely measurable. To such end itis important there be expansion of that section of the scale which' includes the most important range of rate of supply orconsumption of the motor uel;

- for example, the expanded scale section may include those magnitudes of rate of ow as corre- 4spond'with Vthe cruisi;r1grate requirement or consumption of fuel.

The metering unit, Figs. 10-12,may comprise, in eect, the receiver of the telemetric system of Fig. l. It may be placed wherever desired; for aircraft it may be mounted, as upon an instrument board, in the cockpit of an aeroplane, with-v in view o f the pilot or that member of the crew whose duties include predetermining or measuring-with high precision the rate of flow of fuel to a motor or the like.

When there are two or more apparatus, as two or more propelling motors on an aeroplane, there may be provided a transmitter, Fig. 1 or 9, for Veach such apparatus, with provision of switching means, operable by knob la, Fig. 10, for bringing anyone of the transmitters into relation with the receiver, Figs. 1, 10 and 11, common to them all, preferably Vwith utilization of the source of current A in common.

In the receiver unit, within a casing or housing i?, if desired and as shown in Figs. 10 and. 11, is mounted the galvanometer, upper right of Fig. 11y the impedance R2 and its coacting contact K, the scale S, and the index KI, Fig. 10, which moves in unison with contact K.

The scale plate or card S is held in xed position; as indicated in Fig. 10 it is provided with an elongated opening 25 through which the end PI of galvanometer pointer P is visible through .the-glass or other transparent disk D, disposed in front (to the left) of scale S, Fig. 11. Upon the scale card S, at opening 25, is the mark i, i, and at either side thereof may be placed any suitable legend; in the present instance, Lean or` Rich," whereby the operator, when the network N is somewhat out of balance, as indicated by departure of the end PI of the pointer P from alignvment with i, i, is informed of an operating condition, such as the leanness or richness of the gasoaaneen e or adjustable to any desired xed position with respect to disk D. On a stationary circular or cylindrical form 26, concentric with the axis of disk D, Fig.l 11,-is wound the conductor, such as resistance wire, which constitutes the impedance R2, Fig. 1; bearing upon that conductor R2, and mounted upon shaft d, which is driven through disk D rotated by member 5, is contact K, in unison with which rotates index Ki coacting with scale S; Iaccordingly manipulation of knob i rotates both the contact K with respect to impedance R2 on form 26, and index Ki, on member D, with respect to scale S; lmember D and contact K are so rotatable through an arc preferably at least suiiicient to correspond with the entire arcuate length, e. g., about 270, of the scale S; the length of that arc may be greater or less lthan 270, and is dependent upon the length of travel of the core structure. 1n consequence lthe operator may choose or predetermine a rate of'ow of the liquid discharged from member i2, Fig. 9, and by knob il set the index Ki, Fig. l0, to that reading of the scale corresponding with such desired rate of flow; he may then by throttle increase or decrease the rate of ow of the liquid, for example gasoline tovr an aeroplane motor, until the network N becomes balanced, as will be indicated, Fig. l0, by coincidence of pointer ele-l ment Pi with the mark 11i; and having so predetermined the rate of ow by setting of index Kl, if that rate for any cause should increase slightly or decrease slightly, it will become apparent by the slight unbalance oi the network N as evi-- Y measured by rotating knob' to that position which balances-the network, and the rate of-fiow read on scale S opposite to index Kl.

In' general, the length of the core structure (unitary as in Figs. l, 7 and 9, or composite as in Fig. .8) with respect to the lengths of the coils is such that there is always, throughout the range of travel of the core structure, some portion of the core'` structure simultaneously within both of the coils L and LI; otherwise there would occur a reversal of phase as between the cur- `rents through the field windings F, F and the coil G of the galvanometer, with result` the balance of the `network attained under such condition would give an entirely erroneous \scale -.reading; and, importantly, unless there always corresponding respectively with zero or other low be some portion of the core structure simultaneously within both of the coils L, Li, as aforesaid, the scales of Figs. 3, 4, 5, 6 and 10 would be unsuitable, in the sense that the ends thereof magnitude of the condition and the upper end of the scale. corresponding with'maximum magnitude of the condition, would, to be useful, have to be relatively reversed or interchanged; which means that with the readings increasing in al1 said figures in clockwise direction, the scale card in the meter, either as indicated in Fig. 1, or in Figs. 10 and 11, would be wholly erroneous.

Aside from the foregoing, however, by relating v the length of the core structure to the length of its travel in such way that, as aforesaid, there is always some portion of the core structure simultaneously within both coils L, LI, it is possible, because the coils are of unequal length, to change in any selected or desired portion or portions of the total length or range of the scale possible non-proportionality of the movements.

of the contact K to the concurrent ratios of the inductances of the coils. Accordingly, the scales S may, by application of aforesaid principle, be modified, as may be suitable o r desired, vfrom uniformity such as indicated in Fig. 2, to be non-uniform (in any of the respects and to any extents, generically exemplified by Figs. 3-6 and l0) and to be expanded or compressed' in any desired section or sections.

By increasingthe length of coil L with respect to the length of Ll, in Figs. 1, 7, e and 9, the scale will have the characteristic generically indicated by Fig. 3 which is open or expanded at the high reading end and compressed at the other end.

Reversing the positions oi thecoils L and Li, from the relation indicated in Fig. 9, i. placing the longer coil L at the bottoni and the shorter coil Ll above it, there is produced on the scale S great expansion at the lower reading end, liig. 4l, with crowding or compression at the higher reading end.

What we claim is:

l. A measuring system comprising a network, inductance coils of diierent lengths connected, respectively, in different arms oi the networlr, core structure movable with respect'to said coils in response to changes in magnitude of a condition, a source of alternating currentl in a conjugate conducto;` oi the network, means connected in another conjugate conductor oi the riet= work for' indicating balance thereof, impedances connected respectively in different further arms of the network, contact structure engaging said impedances for adjusting the relative magnitudes thereof for balancing the network, a scale which is non-uniform in dependence upon the dif"J ference between the lengths of said coils, and an index movable with said impedance-adjusting contact structure and with respect to said scale for evaluating the magnitudes oi said condition.

2. A measuring system comprising a network, substantially axially spaced inductance coils of 4ciiferent lengths connected, respectively, in di1- `ferent arms of the network., core structure mov able with respect to said coils in response to changes in magnitude oi a condition, a source or" alternating current in a conjugate conductor ci the network, means connected in another conjugate conductor of the network for indicating balance thereof, impedances connected respectively in diierent further arms oi the neti,

work, contact structure engaging said impedances for adjusting the relative magnitudes thereof for balancing the network, a scale having a portion expanded in dependence upon. aforesaid different colllengths and an index movable with said impedance-adjusting contact structure and with respect to said scale for evaluating the magnitudes of said ccnetiition.v

3. A measuring system comprising a network, coils of substantially equal induc'tances and oi e., by

different lengths connected, respectively, in difierent arms of the network, said arms having substantially equal resistances, core structure movE able` with respect to said coils in response to changes in magnitude of a condition, a source of alternating current in a conjugate conductor of the network, means connected in another conjugate conductor of the network for indicating balance thereof, impedances connected respectively in diierent further arms of the network, contact structure engaging said impedances for adjusting the relative magnitudes thereof for balancing the network, a scale which is non-uniform in dependence upon the difference between the lengths of said coils, and an index movable with said impedance-adjusting contact structure.

and with respect to said scalefor evaluating the magnitudes of said condition.

4. A measuring system'comprising a network, inductance coils of different lengths connected,

respectively, in different arms of the network, core structure movable with respect to said coils in response to changes in magnitude of a condition, a source oi alternating current in a conjugate conductor of the network, means connected in another conjugate conductor of the network for indicating lbalance of the network, impedances connected respectively in dierent further arms or" the network, Contact structure engaging said irnpedances for adjusting the relative magnitudes thereof `for balancing the network, a scale and an index movable, in unison with said contact structure, along said scale, distances unequal, in dependence upon aforesaid. different coil lengths, per unit change in the magnitude of said condition.

5. a measuring system comprising a network, inductance coils of different lengths connected, respectively, in different arms or" the4 network, core structure movable with respect to said coils in response to changes in magnitude of a condition, a source of alternating current in a conjugate conductor or the network, means connected in another conjugate conductor of the network for indicating balance thereof, impedances con.n nested respectively in dierent further arms ot the network, Contact structure engaging said irnpedances for adjusting the relative magnitudes thereof for balancing the network, a non=uniiorrn scale whose length is dependent upon the length ci travel of said core structure, and a section whereof is expanded in dependence upon aforosaid dinerent coil lengths, and. an index movable with said impedance-adjusting contact structure and with respect to said scale or evaluating the 'y magnitudes oi said condition.

o. s. measuring system comprising a network, inductance coils of dierent lengths connected, respectively, in different arms of the network, core structure movable with respect to said coils in response to changes in magnitude of a condition, a source of alternating current in a conjugate conductor o the networl, means connected in another conjugate conductor o the network for indicating balance thereof, impedances connested respectively in dierent further arms of the network, Contact structure engaging said im= pedances for adjusting the relative magnitudes thereof lor balancing the network, a scale hav ing, in dependence upon the difference in length having to both sides thereof sections which are compressed, and an index movable with said irigoedance-adjusting contact structure and with reasiatico l spect to said scale for evaluating the' magnitudes of said condition.

'7. A measuring system comprising a network,

inductance coils of different lengths connected,

tion, a source of alternatingcurrent in a con-l jugate conductor or' the network, means connected in another conjugate conductor of the network for indicating balance thereof, impedances connected respectively in dierent further arms of the network, contact structure engaging said irnpedances for adjusting the relative magnitudes thereof for balancing the network, a scale the spacing of whose markings, in dependence upon aforesaid diierence between lengths of coils, progressively decreases from one end thereof to the other, and an index movable with said impedance-adjusting contact structure and with respect to said scale for evaluating the magnitudes of said condition.

8. A measuring unit comprising a xed scale, a transparent disk through which the scale is readable, an indexcarried by said disk andcoacting with said scale, a measuring circuit, a deiecting meter in said circuit, a pointer deflected by said meter, said scale having a mark with respect to which said pointer deects, an impedance included in said circuit, a contact adjustable along said impedance for determining the deflection of said pointer, and a manually operable member for rotating said disk and said contact in unison. 9. A measuring unit comprising a xed scale, a transparent disk through lvwhich the scale is readable, an index carried by said disk and coacting with said scale, a measuring circuit, a defiecting meterv in said circuit, a pointer deiiected by said meter,- lsaid scale having a mark with respect to which said `pointer deec'ts, an impedance includedin said circuit, a contact adjustable along said impedance for determining the deflection of said pointer, said scale having an aperture through which and said disk the pointer is visible, .and manually V`operable means for rotating said disk and adjusting said contact in unison.

10. A measuring system comprising a network,

11. A measuring system comprising a network, inductance coils of different lengths connected, respectively, in diiierent arms of the network, a movable core structure whose movements with respect to said coils, in response vto changes in magnitude of a condition, are proportional to said changes in magnitude of said condition, a source.

of alternating current in a conjugate conductor of the network, means connected in another conjugate conductor of the network forindicating balance thereof, impedances connected respectively in different vfurther arms of 'the network, manually operable contact structure engaging said impedances for adjusting the relative magnitudes thereof for controlling balance of the network, a scale, representative of said magnitudes of said condition, whichis non-uniform in dependenceupon the dierence between the lengths of said coils, and an index moved in unison with said contact structure and relatively to said scali. for evaluating the magnitudes of said condition.

l2. A measuring system comprising a network, inductance coils of dierent lengths connected,

respectively, in different arms of the network, a

coils whose inductances are substantially equal l and of different lengths connected, respectively, in diierent arms of the network, said arms having substantially equal resistances, a core structure of substantially uniform cross section movable with respect to said coils in response to changes in magnitude of a condition, a source of alternating current in a conjugate conductor of the network, means connected in another conjugate conductor of the network for indicating balance thereof, impedances connected respectively in diiferent further arms of the network, manually operable contact structure engaging said impedances for adjusting the relative magnitudes thereof for controlling balanceof. the network, a scale, representative of said magnitudes of said condition, which is non-uniform in dependence upon the difference between the lengths of said coils, and an index moved in unison with said contact structure and with respect to said scale for evaluating the magnitudes of said condition. i

core structure movable with respect to said coils in response to changes in magnitude of a condition, a source of alternating currentin a conjugate conductor of the network, means connected in another conjugate conductor of the network for indicating balance thereof, impedances connected respectively in dierent further arms of the network, a manually operable member for adjusting the relative magnitudes of said impedances for balancing the network, a iixed scale representative of said magnitudes of a condition and associated with said manually operable adjusting member, a second member having an index which coacts with said scale, said balanceindicating means having a pointer deflecting with respect to a mark on said scale,.and manually operable means for actuating said second member and said impedance adjusting means in unison.

13. A system for determining rate of ilow of a uid comprising a network,` inductance coils of diiferent lengths connected, respectively, in diierent arms of the network, means responding to change in the rate of iow of a iiuid by movement of extent proportional to said change, core structure moved with respect to said coils in accord with the movement of said means, a source ofV alternating current in a conjugate conductor of the network, means connected in another conjugate conductor of the network for indicating balance thereof, impedances connected respectively in diierent further karms of the network, manually operable contact structure lengaging said impedances for adjusting the relative magnitudes thereof for controlling balance of the network, a scale, representative of the magnitudes of rate of ow, which is non-uniform in dependence upon the diierence betweerithelengths of said coils, and an index moved in unison with said contact structure and relatively to said scale for evaluating the magnitudes of said condition.

WILLIAM MELAS. JOSEPH RAZEK. 

